Heterogeneous environments can create differential selection pressures among populations, which may result in the evolution of local adaptations. Premating isolation mechanisms may emerge due to limited movement among locally adapted individuals, thus further enhancing such adaptations. The song of male songbirds is one potential premating isolation mechanism that has long been of interest because of its implications for mate choice, local adaptation, and speciation associated with environmental heterogeneity. We tested whether locally adapted mountain chickadees exhibit variation in song structure along an elevation gradient and whether song structure shifts with the distinct change in winter climate severity around the snowline. These birds exhibit large elevation-related differences in numerous behavioral and neurological traits, including variation in spatial cognition associated with fitness consequences. We recorded song along two continuous elevation gradients and detected significant differences among the sampling sites along an elevation gradient and between “high” and “low” elevation songs. Our current results, coupled with previously reported winter climate-related differences are generally consistent with the local adaptation hypothesis explaining geographic variation in song, which suggests that variation in song structure could serve as an indicator of local adaptation. Our study shows that song differences can evolve on a small spatial scale along a continuous species distribution when there is a rapid change in environmental conditions also favoring the evolution of local adaptations. Local adaptations may evolve when heterogeneous environments result in differential selection on fitness-related traits. If locally adapted populations experience reduced movement, additional traits may also change over time and serve as indicators of origin. The ability to identify and mate with local males, which are likely adapted to the prevailing environment, should procure a fitness advantage such that offspring produced with a local individual will inherit the genetic material that made that individual successful. Temperate male bird song is initially learned near the nest, varies geographically, and is commonly used by females to assess male quality. Using mountain chickadees that inhabit an elevation gradient associated with large phenotypic differences, we found significant variation in song structure along an elevation gradient and that male song also changes significantly at an important ecological threshold, consistent with high- and low-elevation songs that may be used by females to identify and mate with local males.

中文翻译：

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鸣禽沿海拔梯度的歌曲结构变化

异质环境会在种群之间产生不同的选择压力，这可能导致局部适应的演变。由于在当地适应的个体之间的活动有限，可能会出现预隔离机制，从而进一步增强这种适应。雄性鸣禽的鸣叫是一种潜在的早产隔离机制，长期以来一直受到关注，因为它对配偶选择、当地适应和与环境异质性相关的物种形成有影响。我们测试了当地适应的山雀是否在海拔梯度上表现出歌曲结构的变化，以及歌曲结构是否随着雪线周围冬季气候严重程度的明显变化而变化。这些鸟类在许多行为和神经学特征上表现出与海拔相关的巨大差异，包括与健康后果相关的空间认知变化。我们沿着两个连续的海拔梯度记录歌曲，并检测到沿海拔梯度的采样点之间以及“高”和“低”海拔歌曲之间的显着差异。我们目前的结果，加上先前报告的冬季气候相关差异，通常与解释歌曲地理变化的局部适应假设一致，这表明歌曲结构的变化可以作为局部适应的指标。我们的研究表明，当环境条件发生快速变化也有利于局部适应的进化时，歌曲差异可以沿着连续的物种分布在小空间尺度上进化。当异质环境导致对适应度相关性状的差异选择时，局部适应性可能会发生变化。如果适应当地的人群活动减少，其他特征也可能随着时间的推移而改变并作为起源指标。识别当地雄性并与之交配的能力，可能适应普遍的环境，应该获得健康优势，这样与当地个体产生的后代将继承使该个体成功的遗传物质。温带雄性鸟鸣最初是在巢附近学习的，因地域不同而异，通常被雌性用来评估雄性品质。使用栖息在与大表型差异相关的海拔梯度的山雀，